Flexible polymer element as toughening agent in prepregs

ABSTRACT

A flexible polymer element for a curable composition wherein the flexible polymer element is in solid phase and adapted to undergo at least partial phase transition to fluid phase on contact with a component of the curable composition in which it is soluble at a temperature which is less than the temperature for substantial onset of gelling and/or curing of the curable composition; a method for the preparation thereof, a support structure or carrier for a curable composition comprising the at least one flexible polymer element together with reinforcing fibers, configurations of support structures and carriers, methods for preparation thereof, a curable composition comprising the at least one flexible polymer element or the support structure or carrier and a curable resin matrix, a kit of parts comprising the components thereof and a method for selection thereof, a method for preparation and curing thereof, and a cured composite or resin body obtained thereby, and known and novel uses thereof.

The present invention relates to a flexible polymer element for use in acurable composition wherein the element is adapted to dissolve in thecurable composition, a method for the preparation thereof, a supportstructure or carrier for a curable composition comprising the at leastone flexible polymer element together with reinforcing fibres,configurations of support structures and carriers, methods forpreparation thereof, a curable composition comprising the at least oneflexible polymer element or the support structure or carrier and acurable resin matrix, a kit of parts comprising the components thereofand a method for selection thereof, a method for preparation and curingthereof, and a cured composite or resin body obtained thereby, and knownand novel uses thereof.

More particularly the invention relates to a flexible polymer element asdefined in the form of a fibre, film or the like, method for thepreparation thereof, support structure or carrier for a curablecomposition as defined in the form of a fabric or the like, andassociated aspects as defined.

Fibre-reinforced resin matrix composites are widely accepted for use ashigh strength low weight engineering materials to replace metals inaircraft structural applications and the like. These composite materialsmay be made by laminating prepregs comprising high strength fibres, suchas glass, graphite (carbon), boron or the like impregnated with a matrixof typically thermoplastic resin. Important properties of suchcomposites are high strength and stiffness and reduced weight.

Composites must meet very stringent requirements in terms of thoseproperties which are significant in or will affect the safety of thestructure comprising the composite when subject to environmentalconditions including extremes of temperature (thermal cyclingresistance), exposure to ultraviolet and other radiation types, exposureto atmospheric oxygen (oxidation resistance) exposure to moisture andthe like; and additionally when subject to hazards such as exposure tosolvents etc, in addition to the usual requirements to withstand allconceivable load and stress types, resist delamination, fracture and thelike.

Curable compositions comprising a blend of polymer resins and optionallyadditionally comprising reinforcing fibres are characterised byindividual physical and chemical properties of the constituent polymerresins and fibres, whereby compositions may be selected for a specificuse. Typically therefore a thermoset resin component is present whichconfers high solvent resistance, thermal cycling resistance etc. Inaddition a thermoplast resin component is present which confers highlevel of toughness etc, and reinforcing fibres are present which conferhigh levels of stiffness, for reduced weight etc.

Typically the respective resins and the fibres are blended or shaped insuitable manner and cured, and retain their distribution or shape byphysical and in some cases by chemical interaction in a desired endproduct. Nevertheless the blending or shaping is in many casescomplicated by factors such as high viscosity of resins, particularlywhen it is desired to impregnate reinforcing fibres, a short “pot life”(pre-gelling time), obtaining uniform or selective dispersion and thelike.

Recently there has been an emergence of an alternative technology formanufacturing composite parts, which technology is generally referred toas Liquid Moulding (LM). This approach differs from that of conventionalprepreg in that the fibres (dry) are placed into a mould/tool and matrixresin is injected/infused directly into the fibres.

Liquid Moulding (LM) is a generic term which covers processingtechniques such as Resin Transfer Moulding (RTM), Liquid Resin Infusion(LRI), Resin Infusion Flexible Tooling (RIFT), Vacuum Assisted ResinTransfer Moulding (VARTM), Resin Film Infusion (RFI) and the like. Thepotential benefits that LM has to offer over that of a conventionalprepreg route are reduced scrap, reduced lay-up time, a non-dependenceon tack and drape and increased shelf life properties. In practice theuse of LM technology finds its greatest use in specialised operations inwhich complex composite structures (multi components) are required,locally strengthened structures are required by selectively distributingcarbon fibres in the mould and where the need for very large structuresis required e.g. marine applications.

Resin Film Infusion (RFI) combines an LM technology with conventionalprepreg, e.g. in RTM or RFI autoclave curing, individual prepregs arestacked in a prescribed orientation to form a laminate, the laminate islaid against a smooth metal plate and covered with successive layers ofporous teflon, bleeder fabric and vacuum bag. A consolidating pressureis applied to the laminate, to consolidate the individual layers andcompress bubbles of any volatile that remain. The use of autoclavecreates a limit to the size of the components that is possible toproduce. Currently for example is not possible to build a boat hull, ayacht or a bridge using an autoclave because that would require a hugepressurized autoclave adding enormous capital costs and running costs.

VARTM simplifies hard mold RTM by employing only one-sided moulds, andusing vacuum bagging techniques to compress the preform. However mouldfilling times can be far too long, if indeed the resin does not curebefore total fill.

RIFT provides much faster fill times. A ‘distribution media’, being aporous layer having very low flow resistance, provides the injectedresin with a relatively easy flow path. The resin flows quickly throughthe distribution media, which is placed on the top of the laminate andthen flows down through the thickness of the preform. The use of fibresto create channels for the resin infusion is known (WO0102146A1(Plastech), U.S. Pat. No. 5,484,642 (Brochier), U.S. Pat. No. 5,326,462(Seemann)) however these remove the channels are either removed duringthe degassing and curing stage or if they are left in they remain intactpost cure.

One of the problems experienced by end users is that it is currentlyvery difficult to manufacture quality components by RIFT or VARTM out ofthe autoclave. Curing with vacuum only or with no pressure cause thecomponents to have very high void content thus leading to poormechanical properties.

We have now surprisingly found a method to obtain composite panelsmanufactured with VARTM and RIFT cured with atmospheric pressure orvacuum only that are easy to inject and show a void content close to 0%.The invention provide the use of fibres during degassing which areabsent in the final cured component.

A common disadvantage concerning the prepreg and LM technologies is inthe area of very tough composite materials. The very nature of theimpregnation or injection process of the resin into the fibrereinforcement e.g. carbon fibre fabrics, requires that its Theologicalproperties, viscosity and elasticity, are able to allow infiltration ofthe resin, throughout the fabric. This is essential if the resultingcomposite structure is to be free of voids and if long impregnation orinjection/infusion times and high injection temperatures are to beavoided.

Resin systems which have high impact performance usually containthermoplastic toughening agents or the like which increase the viscosityand elastic properties of the resin making it very difficult toimpregnate or inject. High impregnation and injection temperatures andpressures are required to make this possible.

A potential way to efficiently provide thermoplastic toughenedcomposites is to remove the thermoplastic from the resin matrix andapply it in some way directly in or onto the fibres or fabric. This canbe achieved using several approaches.

In the case of LM technology, in which complex shapes are manufacturedby applying a binder to the preform as a powder, liquid or film to fixthe preform shape, prior to injecting the thermoplastic and resinmatrix, it is difficult to get any significant quantities ofthermoplastic and matrix into the preform, and excessively hightemperature and pressure are required. Moreover composite materials thuspossess only moderate increases in toughness, since there is a limit tothe amount of thermoplastic which can physically be injected, and maysuffer from the presence of the binder, if incompatible with the matrix.

It is also known for example in EP 392939 to prepare pre-preg withreinforcing fibres by weaving or comingling with thermoplastic fibresand melting to impregnate. These systems do not however attempt tointroduce an additional matrix into the prepreg, and typically employvery high molecular weight thermoplastic polymer, which requiresexcessively high temperature and pressure to melt.

It has been proposed to use hybrid matrix thermosetting resins includinga high molecular weight thermoplastic polymer, as a particulatedispersion as disclosed for example in GB-A-2060490, or as a particulatecoating or film interleave of the fibre-reinforced matrix resin prepregsas disclosed in U.S. Pat. No. 5,057,353. Nevertheless dispersion istypically poor due to difficulty in controlling distribution ofparticles and uniformity of particle size which can influence rate anddegree of melting, and the barrier effect of a continuous film presentin the matrix. U.S. Pat. No. 5,288,547 discloses prepregs for curablecompositions comprising thermoplastic polymer membrane interleave whichis porous. The membrane is incorporated in the prepreg duringpreparation, the membrane laid up against a sheet of reinforcing fibreand melting at elevated temperature and pressure to impregnate thefibres; alternatively prepreg is laid up with membrane therebetween andmelted to impregnate prior to curing to form a composite part;alternatively the membrane is proposed for RTM application laid upbetween layers of dry fibre in a mould, melted to impregnate, and liquidresin injected into the mould.

While this goes some way to alleviating the extreme conditions required,there is still a need for a more versatile solution enabling improvedblending of components and more flexibility and control of nature andamount of dispersions. Specifically the thermoplastic and resin matrixpreclude the possibility to pre-blend and do not blend or diffuseeffectively on curing. Moreover there is a need to introduce greateramounts of highly viscous polymers into the system, such as tougheningagents for example thermoplastics.

We have now surprisingly found that we are able to provide typicallyhigh viscosity polymers in composite structures in manner to overcomethe problems above described, by provision as a soluble flexible polymerelement in solid phase. This is surprising since it would be expectedthat the properties of solubility at relatively low temperature and ofcohesion (as a coherent element) are mutually exclusive, i.e. requiringlow and high MW respectively or an ineffective compromise thereof.

We have moreover found a way to provide a support structure or carrierfor a curable composition comprising a flexible polymer element in whichfibres are held in a desired configuration, without use of a mould, bythe element, which dissolves and disperses in the curable compositionprior to or at the start of the curing process.

It has long been known to prepare synthetic fibres such as viscose,nylons, flame retardant polymers and the like which are used in thetextile industry, woven as fabrics, having good drape and fibrestrength. Whilst some of these may prove in fact to be soluble in aresin matrix according to the present invention, this behaviour has notas yet been observed, the benefits of solubility have to date not beenperceived and the fibres presented in the form of a support structure orcarrier as hereinbefore defined, in turn put to use in the fabrics or inother industries such as the composites or adhesives industry.

In some reinforced composite technology it is also known to introducethermoplastic polymer in the form of strong stitching such as polyesterto hold complex reinforcing structures together, such as 3-dimensionalnon-crimped fabrics (NCF), so that fibres are held in place in alignmentand orientation during the injection, infusion or application ofthermosetting resin. The stitches are of very high melting point polymersuch as 230° C., which is moreover orientated and therefore quitecrystalline so that melting or solution are not possible, the stitchingremains intact post cure.

This can lead to a number of problems such as the moisture sensitivityof the stitch, coefficient of thermal expansion mismatch, shrinkage,loss of mechanical and environmental performance and generalincompatibility of the stitch with the cured thermosetting resin, aswell as aesthetic concerns due to the roughened or patterned surface ofthe finished articles.

There is a need for an improved polymer stitching to hold fibre andfabric structures in place for injection or infusion and curing, whichdoes not deleteriously affect mechanical properties of the curedcomposite.

We have now surprisingly found that flexible polymer elements may beprovided in the form of fibres and the like, which are useful forstitching, which dissolve in the curable composition.

We have also surprisingly found that compositions may be providedcomprising elevated levels of viscous component polymers, by means ofproviding the viscous polymer in both fluid form and in flexible polymerelement solid phase form.

Accordingly in the broadest aspect of the invention there is provided aflexible polymer element for a curable composition wherein the flexiblepolymer element is in solid phase and adapted to undergo at leastpartial phase transition to fluid phase on contact with a component ofthe curable composition in which it is soluble, at a temperature whichis less than the temperature for substantial onset of gelling and/orcuring of the curable composition.

Reference herein to a flexible polymer element is to any shaped elementwhich is both chemically and physically adapted to be at least partiallydissolved in a resin matrix making up the curable composition wherebythe polymer is dispersed at least partially into the matrix as a commonphase by dissolution whereby it loses at least partially its physicalelement form to the curable composition.

Suitably the at least one flexible polymer element is elongate in atleast one direction for example comprises a textile such as a mono ormulti fibre or filament, ribbon, film or mixtures or weave thereof.

Suitably the flexible polymer element is adapted to dissolve during thepreliminary stages of the curing process, during temperature ramping tothe temperature for onset of gelling and/or curing, whereby thecomposition is held in desired configuration by the flexible polymerelement until the curable component viscosity increases, obviating theneed for support by the flexible polymer element or by a mould.

The flexible polymer element may be adapted for use in the presentationor processing of the curable composition whereby the dissolved polymertherefrom may be substantially undetectable and insignificant in theproperties of the cured composition. It is a particular advantage thatflexible polymer elements may be provided which are soluble and may betraceless in the cured product, yet strong enough for use in supporting,carrying or assembling other composition components. Alternatively theflexible polymer element may be for use as a component of the curablecomposition and adapted to contribute to the properties of the endproduct. It is a further advantage that curable compositions may beprovided in which viscous polymers may be included making up asignificant part of the polymer phase of the end product. Alternativelythe flexible polymer element may be for use in the processing of acurable composition with improved composite properties, and may betraceless or otherwise in the final cured product.

In a particular advantage of the present invention the fluid phase ofthe flexible polymer element undergoes excellent dispersion by solvatingeffect of curable component. This is particularly important to theproperties of the cured product. We have surprisingly found thatscanning by Raman spectroscopy at co-ordinates throughout the curedproduct shows 100% dispersion, with identical scans at each co-ordinate.

In a further advantage of the present invention flexible polymerelements provide an excellent outlife and remain in solid phase atambient or elevated temperature, up to 300 or 400° C., in the absence ofdissolving resin, and can be left for years at or below thistemperature, without advance of the composition, and can thereafterundergo phase transition as desired by contact with dissolving resin andcuring under conditions as hereinbefore defined, for exampletemperatures in excess of 60° C., for example of the order of 140° C.

Phase transition is by solution, optionally assisted by heat, in a resinmatrix component of the curable composition. It is a particularadvantage that that soluble polymer elements enable improved blending.

The polymer of the flexible element may be adapted to form a commonphase on curing of the curable composition, e.g. in solution in thethermosetting resin or may wholly or partially phase separate to producea two phase matrix resin system. It is well documented for example in EP311 349 that the toughness of the thermoset/thermoplastic blends isrelated, among other things, to the morphology and phase sizes in thecured blend. The desired level of matrix resin toughness is obtainableby control of the morphology and phase sizes in thethermoset/thermoplastic blend through the chemistries of thethermoplastic polymer and the thermosetting resin precursors, as well asthe other parameters of any desired morphology.

FIGS. B1 and B4 illustrate the process of dissolution, and phaseseparation in the case of a fibre as flexible polymer elementcharacterised by complete dissolution. In FIG. B4 is shown typical twophase morphologies obtained in thermoplast/thermoset systems, which maybe obtained according to the present invention. Phase transition e.g.solution of flexible element may be determined or monitored with use ofany suitable techniques, for example TEM, SEM and the like and suchtechniques may be employed by those skilled in the art to determinesuitable flexible element characteristics and curable compositioncharacteristics and processing conditions for commercial production ofcured compositions.

The polymer forming the flexible polymer element is preferably adaptedto undergo phase transition, i.e. to at least partially dissolve in theresin matrix at a temperature Ts in a range at least part of which isless than the cure temperature of the resin matrix Tc. The polymerelement may be configured in manner to improve or hinder thermalconductivity and speed or slow transfer of heat into the element toendure rapid or delayed solution thereof.

The polymer element may undergo complete or partial phase transition,e.g. may completely dissolve, or may partially dissolve whereby aportion thereof is dispersed into the matrix and a portion retains itselemental form, either by ensuring that precuring time and temperatureare insufficient for complete dissolution or preferably by providing thepolymer as a blend or co-polymer with one or more further insolublepolymers, for example in the form of a random or block co-polymer orother blend or derivative with organic or inorganic substrates. By thismeans the polymer element may be combined with one or more furtherpolymers or other soluble or insoluble organic or inorganic substratesin the cured composition.

The flexible element may contain for example conventional tougheningagents such as liquid rubbers having reactive groups, aggregates such asglass beads, rubber particles and rubber-coated glass beads, metalparticles such as Ti, Al or Fe, filler such as polytetrafluorethylene,silica, graphite, boron nitride, clays such as mica, talc andvermiculite, pigments, nucleating agents, and stabilisers such asphosphates; agents for increased solvent resistance such as F-containingagents, flame retardants such as metal oxides FeO & TiO crystallinepolymers incorporated as blend or as block or random copolymer forexample polyether ketones; conventional binder such as low MW thermosetmonomers for example epoxy, acrylic, cyanate, ester, BMI-type polymersand the like; conventional adhesives such as epoxy polymers and thelike; conventional coating agents etc.

Preferably particles, beads and the like have size in the nm and micronrange, according to the thickness or diameter of the flexible polymerelement, preferably clay particles are 0.5 to 5 nm e.g. 0.1 nm, Tiparticles may be 1–6 micron e.g. 2 micron.

It is a particular advantage of the invention that such conventionaltoughening agents, for example a few percent of high MW rubbers such asNippol and the like make conventional blends highly viscous, theflexible polymer element of the present invention serves as an excellentcarrier whereby concerns such as viscosity, incompatible polymer melttemperatures and the like are overcome.

In the case that uniform distribution of polymer from the flexiblepolymer element is desired, preferably the flexible polymer element isin a form suitable for intimate mixing with other component(s) of acurable composition, e.g. in the form of a fibre, filament, ribbon, orthe like, and in the case that local distribution is desired theflexible polymer element may be in any of these forms or in any otherform suitable for non-intimate presentation in the other component(s),e.g. a film for coating, adhesion or local effect, e.g. tougheningreinforcement.

The flexible element preferably is a fibre or filament having diameterd, or is a film or ribbon having thickness t wherein d or t are in therange up to 100 micron, preferably from 1 to 80 micron for example 30–80micron, more preferably 30–65 micron. Flexibility is a compromisebetween element thickness or diameter and polymer modulus.

Fibres may be provided in desired Tex (weight fibre in g/m fibre,indicating the linear density) which may be in the range 5–150 Tex, andis controlled in known manner during the fibre preparation.

The element is preferably characterised by a % elongation to break inthe range 1–75, preferably 3–50% lower for stitching application andhigher for weaving application, conferred by polymer type and by themethod of manufacture, e.g. stretching and orientation; also bytoughness measured as Dtex, the linear density based on element, e.g.fibre weight per unit length.

Suitably the flexible polymer element is conformable, deformable,drapeable or manipulateable in suitable manner to be presented in acurable composition as hereinbefore defined. Without being limited tothis theory it is thought that physical interactions are created duringthe manufacture of the polymer element which induce or enhanceflexibility to particularly advantageous effect by virtue oforientation, chain interaction, individual polymer chain characteristicsand the like, contributing to elastomeric behaviour and properties ofstretch and strength, enabling knotting, stitching, winding and thelike.

The flexible polymer element may be characterised by binding or adhesionproperties, for example conferred by softening above ambienttemperatures, or comprising monomers for example thermoset (epoxy)monomers or other known binders, to assist in the physical associationin a curable composition as hereinbefore defined. In this manner theflexible polymer element of the invention is particularly suitable foruse in LM technology as hereinbefore defined.

In principle, any polymer which is at least partially soluble in acurable, eg a thermosetting, matrix resin below its curing temperatureand which may be formed into a flexible element as hereinbefore definedby known or novel means, such as extrusion, spinning, casting etc., maybe employed in the practice of the invention. Preferably the flexiblepolymer element comprises a polymer having elastomeric properties at orabove its glass transition temperature or softening temperature, and isselected from natural or synthetic rubbers and elastomers,thermoplastics and mixtures, miscible or immiscible blends thereof orrandom or block copolymers with other amorphous or crystalline polymersand/or monomers. More preferably the flexible element comprises anamorphous polymer having elastomeric properties additionally below itsglass transition temperature or softening temperature, more preferablycomprises a thermoplastic polymer. Useful thermoplastic include polymerssuch as cellulose derivatives, polyester, polyamide, polyimide,polycarbonate, polyurethane, polyacrylonitrile, poly(methylmethacrylate), polystyrene and polyaromatics such as polyarylethers,polyarylketones and particularly polyarylsulphones. Copolymers may alsobe used such as polyesteramide, polyamideimide, polyetherimide,polyaramide, polyarylate, poly(ester) carbonate, poly(methylmethacrylate/butyl acrylate), polyethersulphone-etherketone. Polymerblends may also be used.

Polyurethanes include thermoplastic polyurethane rubber. Polyamidesinclude nylon and other axis oriented long chain polymers which can beformed into filament or film, polyester includes the straight chaincondensation product of terephthalic acid and ethan-1, 2-diol(polyester), poly acrylates includes acrylic fibres synthesised from aplurality of monomers including at least 85 wt % acrylonitrile,cellulose derivatives include cellulose diacetate, viscose fibres,polyetherketones are based on bisphenol A.

Preferably the thermoplastic is a polyaromatic. Preferably thepolyaromatic polymer comprises same or different repeating units of theformula:—X—Ar—A—Ar—X—

-   -   wherein A is selected from SO₂, a direct link, oxygen, sulphur,        —CO— or a divalent hydrocarbon radical;        -   X is a divalent group as defined for A, which may be the            same or different, or is a divalent aromatic group such as            biphenylene;    -   Ar is an aromatic divalent group, or multivalent including any        one or more substituents R of the aromatic rings, each R        independently selected from hydrogen, C₁₋₈ branched or straight        chain aliphatic saturated or unsaturated aliphatic groups or        moieties optionally comprising one or more heteroatoms selected        from O,S,N, or halo for example Cl or F; and groups providing        active hydrogen especially OH, NH₂, NHR— or —SH, where R— is a        hydrocarbon group containing up to eight carbon atoms, or        providing other cross-linking activity especially epoxy, (meth)        acrylate, cyanate, isocyanate, acetylene or ethylene, as in        vinyl, allyl or maleimide, anhydride, oxazoline and monomers        containing saturation; and    -   wherein said at least one polyaromatic comprises reactive        pendant and/or end groups, preferably selected from reactive        heteroatom, heteroatom containing or cross-linking groups as        defined for R.

Specifically the at least one polyaromatic comprises at least onepolyaromatic sulphone comprising ether-linked repeating units,optionally additionally comprising thioether-linked repeating units, theunits being selected from the group consisting of-(PhAPh)_(n)-and optionally additionally-(Ph)_(a)-

-   -   wherein A═CO or SO₂, Ph is phenylene, n=1 to 2 and can be        fractional, a=1 to 4 preferably a=1, 2 or 3 and, can be        fractional and when a exceeds 1, said phenylenes are linked        linearly through a single chemical bond or a divalent group        other than —CO— or —SO₂— or are fused together directly or via a        cyclic moiety, such as acid alkyl group, a (hetero) aromatic or        cyclic ketone, amide, imide, imine or the like.

Preferably the polyaromatic comprises polyether sulphone, morepreferably a combination of polyether sulphone and of polyether ethersulphone linked repeating units, in which the phenylene group is meta-or para- and is preferably para and wherein the phenylenes are linkedlinearly through a single chemical bond or a divalent group other thansulphone, or are fused together. By “fractional” reference is made tothe average value for a given polymer chain containing units havingvarious values of n or a.

Preferably the repeating unit -(PhSO₂Ph)- is always present in said atleast one polyarylsulphone in such a proportion that on average at leasttwo of said units—(PhSO₂Ph)_(n) are in sequence in each polymer chainpresent, said at least one polyarylsulphone having reactive pendantand/or end groups.

Additionally, in the polyarylsulphone polymer, the relative proportionsof the said repeating units is such that on average at least two units(PhSO₂Ph)_(n) are in immediate mutual succession in each polymer chainpresent and is preferably in the range 1:99 to 99:1, especially 10:90 to90:10, respectively. Typically the ratio is in the range 75–50 (Ph)_(a),balance (PhSO₂Ph)_(n). In preferred polyarylsulphones the units are:X PhSO₂Ph XPhSO₂Ph(“PES”) and  (I)X(Ph)_(a)XPh SO₂Ph(“PEES”)  (II)

-   -   where X is O or S and may differ from unit to unit; the ratio is        I to II (respectively) preferably between 10:90 and 80:20        especially between 10:90 and 55:45, more especially between        25:75 and 50:50, or the ratio is between 20:80 and 70:30, more        preferably between 30:70 and 70:30, most preferably between        35:65 and 65:35.

The preferred relative proportions of the repeating units of thepolyarylsulphone may be expressed in terms of the weight percent SO₂content defined as 100 times (weight of SO₂)/(weight of average repeatunit). The preferred SO₂ content is at least 22, preferably 23 to 25%.When a=1 this corresponds to PES/PEES ratio of at least 20:80,preferably in the range 35:65 to 65:35.

The above proportions refer only to the units mentioned. In addition tosuch units the polyarylsulphone may contain up to 50 especially up to25% molar of other repeating units: the preferred SO₂ content ranges (ifused) then apply to the whole polymer. Such units may be for example ofthe formula:—Ar—A—Ar—in which A is a direct link, oxygen, sulphur, —CO— or a divalenthydrocarbon radical. When the polyarylsulphone is the product ofnucleophilic synthesis, its units may have been derived for example fromone or more bisphenols and/or corresponding bisthiols or phenol-thiolsselected from hydroquinone, 4,4′dihydroxybiphenyl, resorcinol,dihydroxynaphthalene (2,6 and other isomers),4,4′-dihydroxybenzophenone, 2,2′di(4-hydroxyphenyl)propane and- methane.

If a bis-thiol is used, it may be formed in situ, that is, a dihalide asdescribed for example below may be reacted with an alkali sulphide orpolysulphide or thiosulphate.

Other examples of such additional units are of the formula:-Ph-Q(Ar—Q′)_(n)-Ph-in which Q and Q′, may be the same or different, are CO or SO₂: Ar is adivalent aromatic radical; and n is 0, 1, 2 or 3 provided that n is notzero where Q is SO₂. Ar is preferably at least one divalent aromaticradical selected from phenylene, biphenylene or terphenylene. Particularunits have the formula:-Ph-Q-[-Ph-)m-Q′-]n-Ph-where m is 1, 2 or 3. When the polymer is the product of nucleophilicsynthesis, such units may have been derived from one or more dihalides,for example selected from 4,4′-dihalobenzophenone,4,4′bis(4-chlorophenylsulphonyl)biphenyl,1,4,bis(4-bis(4-halobenzoyl)benzene and 4,4′-bis(4-halobenzoyl)biphenyl.

They may of course have been derived partly from the correspondingbisphenols.

The polyaromatic polymer may be the product of nucleophilic synthesisfrom halophenols and/or halothiophenols. In any nucleophilic synthesisthe halogen if chlorine or bromine may be activated by the presence of acopper catalyst.

Such activation is often unnecessary if the halogen is activated by anelectron withdrawing group. In any event fluoride is usually more activethan chloride. Any nucleophilic synthesis of the polyaromatic is carriedout preferably in the presence of one or more alkali metal salts, suchas KOH, NaOH or K2CO3 in up to 10% molar excess over the stoichiometric.

The polymer may be characterised by a range of MW which may typically bedefined either by Mn, peak MW and other means, usually determined by nmrand gpc. Preferably the polymer is selected in the range up to 70,000for example 9000–60,000 for toughening, and in this case the numberaverage molecular weight Mn of the polyaromatic is suitably in the range2000 to 25000, preferably 2000 to 20000, more preferably 5000 or 7000 to18000, most preferably 5000 or 7000 to 15000.

The polyaromatic is preferably of relatively low molecular weight. Italso preferably contains in-chain, pendant or chain-terminating chemicalgroups which are capable of self-assembling to form higher molecularweight complexes through non covalent bonds with similar or differentchemical groupings in the polymer. These maybe, for example, hydrogenbonds, London forces, charge transfer complexes, ionic links or otherphysical bonds. Preferably the non-covalent bonds are hydrogen bonds orLondon forces which will dissociate in solution to regenerate therelatively low molecular weight precursor polyaromatic. The polyaromaticpreferably contains pendant or chain-terminating groups that willchemically react with groups in the thermosetting resin composition toform covalent bonds. Such groups may be obtained by a reaction ofmonomers or by subsequent conversion of product polymer prior to orsubsequently to isolation. Preferably groups are of formula:—A′—Y

-   -   where A′ is a divalent hydrocarbon group, preferably aromatic,        and Y is a group reactive with epoxide groups or with curing        agent or with like groups on other polymer molecules. Examples        of Y are groups providing active hydrogen especially OH, NH₂,        NHR′ or —SH, where R′ is a hydrocarbon group containing up to 8        carbon atoms, or providing other cross-linking reactivity        especially epoxy, (meth)acrylate, cyanate, isocyanate, acetylene        or ethylene, as in vinyl allyl or maleimide, anhydride,        oxazaline and monomers containing saturation. Preferred end        groups include amine and hydroxyl.

In a particular advantage of the invention the polymer of the flexiblepolymer element may have low molecular weight, but be adapted to reacton curing to provide the higher molecular weight required for effectivetoughening or the like, as disclosed in co-pending GB 0020620.1 thecontents of which are incorporated herein by reference. This is ofparticular advantage since it further alleviates the problems of highviscosity. Specifically the polymer may comprise chains of at least onearomatic polymer or a mixture thereof together with at least one chainlinking component wherein the at least one aromatic polymer comprisespolymer chains of number average molecular weight (Mn) in a first rangeof 2000 to 11000, especially 3000 to 9000 and characterised by a polymerflow temperature, and wherein one of the at least one polyaromatic andthe at least one chain linking component comprises at least one reactiveend group and the other comprises, at least two linking sites reactiveend groups Y and chain linking sites, Z are selected, OH, NH₂, NHR or SHwherein R is a hydrocarbon group containing up to 8 carbon atoms, epoxy,(meth)acrylate, (iso)cyanate, isocyanate ester, acetylene or ethylene asin vinyl or allyl, maleimide, anhydride, acid, oxazoline and monomerscontaining unsaturation characterised in that a plurality of the endgroups are adapted to react with the linking sites at chain linkingtemperature in excess of the polymer flow temperature to form linkedpolymer chains of number average molecular weight (Mn) in a second rangeof 9000 to 60000, especially 11000 to 25000, which is in excess of thefirst range, substantially thermoplastic in nature.

Flow temperature is defined as the temperature at which the polymerattains a suitably fluid state to enable a degree of polymer chainmobility to align itself for reaction. Preferably the flow temperaturecorresponds to a solution temperature at which the polyaromaticdissolves.

Chain linking temperature is defined as the temperature at which thepolymer chain ends reaction is initiated. Preferably the chain linkingtemperature is higher than a product processing temperature, to removesolvent and improve wet out of the prepreg which leads to better qualityprepreg with easier handling characteristics. Preferably the chainlinking temperature corresponds to the gelling or curing temperature.

Chain linking components are preferably selected from the formulaB(Z)nwherein B is an oligomer or polymer backbone or is an aliphatic,alicyclic or aromatic hydrocarbon having from 1 to 10 carbon atoms andoptionally including heteroatoms N, S, O and the like and optionallysubstituted, or is C, O, S, N or a transition metal nucleus or is asingle bond, n is a whole number integer selected from 2 to 10000preferably 2 to 8 or 5 to 500 or 500 to 10000.

Accordingly it will be apparent that self reaction between methacrylateended polymer and chain linking component or between maleimide endedpolymer and chain linking component or between oxazoline ended polymerand chain linking component for example is possible and within the scopeof the present invention.

In one preferred embodiment the reactive end group is hydroxy andcorresponds to a linking site functionality which is epoxy, wherebyreaction thereof produces a β hydroxy ether linkage in polymers ofincreased number average molecular weight having either hydroxy or epoxyend groups as desired. Alternatively, the reactive end group is NH₂ andthe linking site functionality is anhydride, whereby reaction thereofproduces an imide linkage in polymers of increased number averagemolecular weight having NH₂ or anhydride end groups. Alternatively thereactive end group is NH₂ and the linking site functionality ismaleimide. Mixtures of the above may be employed to produce a mixedarchitecture including a plurality of reactive end group-linking sitecombinations.

Preferred linking components include multifunctional epoxy resins,amines and in particular triazines, and anhydrides. Suitable epoxyresins and amines are selected from resins hereinafter defined formatrix resins, and are preferably selected from MY0510, Epikote 828[O(CH₂CH)CH₂OPh]₂C(CH₃)₂ and the Cymel class of epoxies including Cymel0510, benzophenone tetra carboxylic acid dianhydride (BTDA)[O(CO)₂Ph]₂CO, and maleic anhydride.

Preferably flexible elements comprising two or more polymers comprise ablend or copolymer of amorphous polymers or of amorphous and semicrystalline polymer. This is of particular advantage in enabling thepreparation of multiblock compositions having lowered processingtemperatures whilst nevertheless retaining excellent product propertiessuch as solvent resistance.

In a further aspect of the invention there is provided a method for thepreparation of a flexible polymer element as hereinbefore defined byknown or novel methods, for example comprising track etching ormechanical stretching the polymer resin melt, phase precipitationmethods such as immersion, evaporation, solvent casting, thermal andhumidity methods or forming the element from its monomeric precursor andpolymerising.

Preferably elements in the form of fibres or film are obtained bycontinuous extrusion of resin melt onto reels and film forming orspinning as known in the art of synthetic textiles manufacture bymechanical stretching with heating, more preferably by providing thepolymer melt, drawing off in elemental shape, subjecting to a heatingand mechanical stretching regime which may orient polymer chains andrender the element elastomeric and predisposed to dissolution, andcooling, preferably by pulling in air for a desired distance, eg 50 to500 mm. Preferably polymer melt is drawn off through a die head or thelike providing a desired number of apertures or slots, using a pump withcontrolled pump rate for a desired linear density (Tex) of polymer forexample up to 180 Tex.

The element may be prepared from micronised or unmicronised polymer,pellets or other extrudate and the like. Preferably fibres are preparedas multifilaments of up to 20 same or different polymer filaments, whichare drawn off from the molten polymer, cooled and optionally twisted asdesired, and then subjected to heating and stretching. The multifilamentis more resistant to breaking, there is a trade off between higherstrength and lower flexibility in selection of filaments andtwists/meter. Twisting is conventionally used for preparing stitchingfibres, to counteract undesired natural twist and breakage.

In a further aspect of the invention there is provided a supportstructure or carrier for a curable composition comprising at least oneflexible polymer element as hereinbefore optionally defined togetherwith structural elements, preferably reinforcing fibres, wherein the atleast one flexible polymer element is present in solid phase and adaptedto undergo at least partial phase transition to fluid phase on contactwith a resin matrix component of a curable composition in which theelement is soluble, at a temperature which is less than the temperaturefor substantial onset of gelling and/or curing of the curable component.

Reference herein to a support structure or carrier is to a presentationof the polymer element in physical, preferably intimate association withthe reinforcing fibres, for example mono or multi filament fibres,ribbons and/or films are presented as the fibres or ribbons alone orwith reinforcing fibres in a support structure or carrier comprising afabric, web, weave, non woven, overwinding, preform, scrim, mesh,fleece, roving, prepreg, composite or laminar film or interleave or thelike or a mixture thereof, or stitched, sewn, threaded or the likepresentations thereof. Suitably the polymer element serves to supportthe further component(s) of the structure or to carry the reinforcingfibres and/or resin matrix, and optionally any further component(s) of adesired curable composition. The support structure or carrier may bemutually supporting or carrying whereby the at least one flexiblepolymer element is additionally supported by or carried by thereinforcing fibres or an additional resin matrix.

Reference herein to structural or reinforcing fibres is to insolublefibres as known in the art which stiffen composites, such as organic orinorganic polymer, carbon, glass, inorganic oxide, carbide, ceramic ormetal and the like fibres.

The support structure or carrier of the invention may have any number ofphysical presentations.

The support structure or carrier may be in the form of a preform asknown in the art but wherein the flexible polymer element is present asfibres or ribbons amongst the reinforcing fibres in aligned ormis-aligned or stitched fashion or as a multi filament of solublepolymers fibres and reinforcing fibres which may be braided, spun orover wound, or is present as a film laid up against the reinforcingfibres and adhered or crimped or otherwise physically associatedtherewith. Particularly advantageous presentations include non-crimpedfabrics of reinforcing fibre with flexible polymer fibre stitching,preforms of aligned or random reinforcing and flexible polymer fibreswhich may be stitched or punched or softened to confer binding, or otherconfigurations in which flexible polymer element is presented nonuniformly with respect to the reinforcing fibre, to locally conferproperties such as toughening and the like characteristic of theflexible polymer, for example around bolt holes, fastening apertures,high stress panels and the like.

In the case of a comingled structure or carrier comprising flexiblepolymer element and continuous, short or chopped reinforcing fibres theat least one flexible element is a monofilament or low twist/meterhigher multifilament fibre, optionally cut to comparable length andsimply admixed. In the case of a woven or braided structure or carrierwith the reinforcing fibres woven to produce 100% flexible polymerelement fabrics, the element is monofilament or lower multifilament.When the flexible element is used as a stitch it is preferably of lower% elongation. In any case the structure or carrier can be formed at anysuitable stage in the manufacture of the fabric based reinforcements. Itcan also be applied after the manufacture of the fabric for example inthe case where a hole is created in the assembled fabrics (preforms) orto physically stitch multi-component parts together, prior to resininjection/infusion.

In a preferred configuration, a support structure or carrier ashereinbefore defined preferably comprises structural fibres, laid up indesired manner, and fibre form flexible polymer element in the form ofstitching, adapted to undergo phase transition as hereinbefore definedin manner to disperse locally or universally in the curable composition.Suitably the support structure or carrier comprises therefore a fabricin which the structural fibres or fabric are laid up in random, mono ormultiaxial, (co) linear or (co) planar arrangement and the flexiblepolymer element fibres are in the form of stitching in conventionalmanner securing the fibre or fabric or assemblies thereof as desired.Preferably stitching comprises upper and lower thread securing fibres,fabrics or assemblies thereof from opposite faces. The support structureor carrier provides at least partially traceless stitching, preferablyprovides traceless stitching. Suitably the flexible polymer element isprovided in controlled amount with reference to Tex (weight of flexiblepolymer element in grams per 1000 m of structural fibres), given byTex_(fpe)=(% wt_(sf)×% wt_(fpe))÷Tex_(sf).

A number of techniques exist for stitching reinforcing fibres withpolymer stitching which remains in situ post compositing and curing.Specifically:

-   -   (i) tailored fibre placement (TFP) for directional strengthening        involves laying up continuous reinforcing fibre in a desired        direction and following with polymer stitching, in multiple        layers, whereby a first line stitches a single thread or tow of        structural fibre, a subsequent round stitches a superimposed        thread or tow of structural fibre, a subsequent round stitches a        further superimposed thread or tow etc.—this gives generally        poor mechanical properties, one face of the resultant fabric        having multiple round insoluble stitching;    -   (ii) creating folding seams with stitching whereby a line of        stitching is formed along a desired fold line;    -   (iii) stiffening stitching, whereby cross stitching lines placed        in close proximity in a thin fabric layer confer enhanced        stiffness and increased planarity of the fabric;    -   (iv) assembly stitching in which a fabric to be oriented for        example perpendicular to a second fabric is stitched in place;    -   (v) non crimped fabric (NCF) stitching in which cross layers of        fabric are loosely stitched, to give a smooth surface—if the        tension of the stitch is too high the surface loop of the stitch        can however crimp the fabric in the thickness direction,        moreover the stitch can be detected erroneously as a defect in        non-destructive testing rendering the testing unreliable; and    -   (vi) through the thickness (TTF) stitching through the        interlaminar region of a composite with Kevlar fibre stitching        which has been wrapped around with eg polyester fibre, rendering        the Kevlar stitch flexible, strengthening the interlaminar        region and reducing the likelihood of delamination.

In a particular advantage of the present invention all of the aboveknown stitching methods may be provided using the soluble fibre formflexible polymer element, in conventional manner. The stitching ishowever adapted to dissolve on heating at the start of the cure cycleand disperse throughout the fabric, immediately followed by curing. Thisdispersion avoids deterioration of mechanical properties, and in mostinstances enhances mechanical properties by improved distribution of forexample toughening polymer derived from dissolved stitching. Accordinglyin a preferred embodiment the invention provides a support structure orcarrier comprising the above mentioned lay up and stitching,specifically the invention provides traceless stitching.

In a further aspect of the invention there is provided a process for thepreparation of a support structure or carrier as hereinbefore definedcomprising providing at least one flexible polymer element, andproviding reinforcing fibres as hereinbefore defined and combining inmanner to provide a physical association thereof. Combining to provide aphysical intimate association may be by methods as known in the art oftextiles, for example by stitching, knitting, crimping, punching,(uni)weaving, braiding, overwinding, (inter) meshing, comingling,aligning, twisting, coiling, knotting, threading and the like.

A support structure or carrier may be prepared in continuous manner forexample as a roll of fabric which may be tailored by stitching andweaving in desired manner, for example cross stitching to prevent fabricdistortion on handling, provide folding seams, directional strengtheningand the like.

Structural fibres as hereinbefore defined can be short or choppedtypically of mean fibre length not more than 2 cm, for example about 6mm. Alternatively, and preferably, the fibres are continuous and may,for example, be unidirectionally-disposed fibres or a woven fabric, i.e.the composite material comprises a prepreg. Combinations of both shortand/or chopped fibres and continuous fibres may be utilised. The fibresmay be sized or unsized. Reinforcing fibres can be added typically at aconcentration of 5 to 35, preferably at least 20% by weight. Forstructural applications, it is preferred to use continuous fibre forexample glass or carbon, especially at 30 to 70, more especially 50 to70% by volume.

The fibre can be organic, especially of stiff polymers such as polyparaphenylene terephthalamide, or inorganic. Among inorganic fibresglass fibres such as “E” or “S” can be used, or alumina, zirconia,silicon carbide, other compound ceramics or metals. A very suitablereinforcing fibre is carbon, especially as graphite. Graphite fibreswhich have been found to be especially useful in the invention are thosesupplied by Amoco under the trade designations T650-35, T650-42 andT300; those supplied by Toray under the trade designation T800-HB; andthose supplied by Hercules under the trade designations AS4, AU4, IM 8and IM 7, and HTA and HTS fibres.

Organic or carbon fibre is preferably unsized or is sized with amaterial that is compatible with the composition according to theinvention, in the sense of being soluble in the liquid precursorcomposition without adverse reaction or of bonding both to the fibre andto the thermoset/thermoplastic composition according to the invention.In particular carbon or graphite fibres that are unsized or are sizedwith epoxy resin precursor. Inorganic fibre preferably is sized with amaterial that bonds both to the fibre and to the polymer composition;examples are the organo-silane coupling agents applied to glass fibre.

In a further aspect of the invention there is provided a curablecomposition comprising a flexible polymer element or a support structureor carrier as hereinbefore defined and curable resin matrix, togetherwith optional additional reinforcing fibres, and catalysts, curingagents, additives such as fillers and the like.

A matrix resin is preferably a thermosetting resin and may be selectedfrom the group consisting of an epoxy resin, an addition-polymerisationresin, especially a bis-maleimide resin, a formaldehyde condensateresin, especially a formaldehyde-phenol resin, a cyanate resin, anisocyanate resin, a phenolic resin and mixtures of two or more thereof,and is preferably an epoxy resin derived from the mono or poly-glycidylderivative of one or more of the group of compounds consisting ofaromatic diamines, aromatic monoprimary amines, aminophenols, polyhydricphenols, polyhydric alcohols, polycarboxylic acids, cyanate ester resin,benzimidazole, polystyryl pyridine, polyimide or phenolic resin and thelike, or mixtures thereof. Examples of addition-polymerisation resin areacrylics, vinyls, bis-maleimides, and unsaturated polyesters. Examplesof formaldehyde condensate resins are urea, melamine and phenols.

More preferably the thermosetting matrix resin comprises at least oneepoxy, cyanate ester or phenolic resin precursor, which is liquid atambient temperature for example as disclosed in EP-A-0311349,EP-A-0365168, EP-A-91310167.1 or in PCT/GB95/01303. Preferably thethermoset is an epoxy or cyanate ester resin or a mixture thereof.

An epoxy resin may be selected from N,N,N′N′-tetraglycidyl diaminodiphenylmethane (e.g. “MY 9663”, “MY 720” or “MY 721” sold byCiba-Geigy) viscosity 10–20 Pa s at 50° C.; (MY 721 is a lower viscosityversion of MY 720 and is designed for higher use temperatures);N,N,N′,N-tetraglycidyl-bis(4-aminophenyl)-1,4-diiso- propylbenzene (e.g.Epon 1071 sold by Shell Chemical Co.) viscosity 18–22 Poise at 110° C.;N,N,N′,N′-tetraglycidyl-bis(4-amino-3,5-dimethylphenyl)-1,4-diisopropylbenzene,(e.g. Epon 1072 sold by Shell Chemical Co.) viscosity 30–40 Poise at110° C.; triglycidyl ethers of p-aminophenol (e.g. “MY 0510” sold byCiba-Geigy), viscosity 0.55–0.85 Pa s at 25° C.; preferably of viscosity8–20 Pa at 25° C.; preferably this constitutes at least 25% of the epoxycomponents used; diglycidyl ethers of bisphenol A based materials suchas 2,2-bis(4,4′-dihydroxy phenyl) propane (e.g. “DE R 661” sold by Dow,or “Epikote 828” sold by Shell), and Novolak resins preferably ofviscosity 8–20 Pa s at 25° C.; glycidyl ethers of phenol Novolak resins(e.g. “DEN 431” or “DEN 438” sold by Dow), varieties in the lowviscosity class of which are preferred in making compositions accordingto the invention; diglycidyl 1,2-phthalate, e.g. GLY CEL A-100;diglycidyl derivative of dihydroxy diphenyl methane (Bisphenol F) (e.g.“PY 306” sold by Ciba Geigy) which is in the low viscosity class. Otherepoxy resin precursors include cycloaliphatics such as3′,4′-epoxycyclohexyl-3,-4-epoxycyclohexane carboxylate (e.g. “CY 179”sold by Ciba Geigy) and those in the “Bakelite” range of Union CarbideCorporation.

A cyanate ester resin may be selected from one or more compounds of thegeneral formula NCOAr(YxArm)qOCN and oligomers and/or polycyanate estersand combinations thereof wherein Ar is a single or fused aromatic orsubstituted aromatics and combinations thereof and therebetween nucleuslinked in the ortho, meta and/or para position and x=0 up to 2 and m andq=0 to 5 independently. The Y is a linking unit selected from the groupconsisting of oxygen, carbonyl, sulphur, sulphur oxides, chemical bond,aromatic linked in ortho, meta and/or para positions and/or CR₂ whereinR₁ and R₂ are hydrogen, halogenated alkanes, such as the fluorinatedalkanes and/or substituted aromatics and/or hydrocarbon units whereinsaid hydrocarbon units are singularly or multiply linked and consist ofup to 20 carbon atoms for each R₁ and/or R₂ and P(R₃ R₄R′₄R₅) wherein R₃is allyl, aryl alkoxy or hydroxy, R′₄ may be equal to R₄ and a singlylinked oxygen or chemical bond and R₅ is doubly linked oxygen orchemical bond or Si(R₃ R₄R′₄R₆) wherein R₃ and R₄, R′₄ are defined as inP( R₃R₄R′₄R₅) above and R₅ is defined similar to R₃ above. Commerciallyavailable cyanate esters include cyanate esters of phenol/formaldehydederived Novolaks or dicyclopentadiene derivatives thereof, an example ofwhich is XU71787 sold by the Dow Chemical Company, and low viscositycyanate esters such as L10 (Lonza, Ciba-Geigy, Bisphenol derived).

A phenolic resin may be selected from any aldehyde condensate resinsderived from aldehydes such as methanal, ethanal, benzaldehyde orfurfuraldehyde and phenols such as phenol, cresols, dihydric phenols,chlorphenols and C₁₋₉ alkyl phenols, such as phenol, 3- and4-cresol(1-methyl, 3- and 4-hydroxy benzene), catechol(2-hydroxyphenol), resorcinol(1,3-dihydroxy benzene) and quinol(1,4-dihydroxybenzene). Preferably phenolic resins comprise cresol and novolakphenols.

Suitable bismaleimide resins are heat-curable resins containing themaleimido group as the reactive functionality. The term bismaleimide asused herein includes mono-, bis-, tris-, tetrakis-, and higherfunctional maleimides and their mixtures as well, unless otherwisenoted. Bismaleimide resins with an average functionality of about twoare preferred. Bismaleimide resins as thus defined are prepared by thereaction of maleic anhydride or a substituted maleic anhydride such asmethylmaleic anhydride, with an aromatic or aliphatic di- or polyamine.Examples of the synthesis may be found, for example in U.S. Pat. Nos.3,018,290, 3,018,292, 3,627,780, 3,770,691 and 3,839,358. The closelyrelated nadicimide resins, prepared analogously from a di- or polyaminebut wherein the maleic anhydride is substituted by a Diels-Alderreaction product of maleic anhydride or a substituted maleic anhydridewith a diene such as cyclopentadiene, are also useful. As used hereinand in the claims, the term bismaleimide shall include the nadicimideresins.

Preferred di- or polyamine precursors include aliphatic and aromaticdiamines. The aliphatic diamines may be straight chain, branched, orcyclic, and may contain heteroatoms. Many examples of such aliphaticdiamines may be found in the above cited references. Especiallypreferred aliphatic diamines are hexanediamine, octanediamine,decanediamine, dodecanediamine, and trimethylhexanediamine.

The aromatic diamines may be mononuclear or polynuclear, and may containfused ring systems as well. Preferred aromatic diamines are thephenylenediamines; the toluenediamines; the various methylenedianilines,particularly 4,4′-methylenedianiline; the naphthalenediamines; thevarious amino-terminated polyarylene oligomers corresponding to oranalogues to the formula H₂N—Ar[X—Ar]_(n)NH₂, wherein each Ar mayindividually be a mono- or poly-nuclear arylene radical, each X mayindividually be —O—, —S—, —CO₂, —SO₂—, —O—CO—, C₁–C₁₀ lower alkyl,C₁–C₁₀ halogenated alkyl, C₂–C₁₀ lower alkyleneoxy, aryleneoxy,polyoxyalkylene or polyoxyarylene, and wherein n is an integer of fromabout 1 to 10; and primary aminoalkyl terminated di- and polysiloxanes.

Particularly useful are bismaleimide “eutectic” resin mixturescontaining several bismaleimides. Such mixtures generally have meltingpoints which are considerably lower than the individual bismaleimides.Examples of such mixtures may be found in U.S. Pat. Nos. 4,413,107 and4,377,657. Several such eutectic mixtures are commercially available.

Preferably the flexible polymer element and dissolving matrix areselected as a “solution pair” providing not only dissolution at desiredtime and temperature, but also good matrix injection, dispersion,morphology such as phase separation and traceless dispersion if desired,and the like. Suitable solution pairs include a low viscosity matrixresin for good injection and rapid dissolution, and compatibility ofmatrix rein and element resin. Alternatively or additionally lesscompatible resins may be used if it is desired to introduce phaseseparation for enhanced mechanical properties. Combinations of differentviscosity resins may be used each contributing various of the aboveproperties where these are not provided by a single resin.

In the curable composition the flexible polymer element may be presentas fibres in the form of a prepreg with the matrix resin in knownmanner, as a film in the form of an interleave with matrix film or as aporous or foamed film impregnated with matrix resin or the like.

The present invention is of particular advantage in the case that theflexible polymer element comprises in fluid phase a highly viscouspolymer or a precursor thereof. The curable composition preferablycomprises at least one curable thermoset matrix resin as hereinbeforedefined and optionally at least one thermoplast matrix resin.

Such compositions confer enhanced beneficial properties in the endproduct, whereby composites may be provided to higher specification.Traditionally this may be achieved simply by incorporating additives orby increasing the quantity of a component. However it has provedproblematic to increase the quantity of high viscosity resins beyond alimiting amount at which it is no longer possible to achieve a highquality blend with the additional composition components, and manyproperties of such resins cannot be conferred by other materials oradditives. This is particularly the case with viscous thermoplasticresins, in preparing high strength low weight engineering materials.

In the case that the resin matrix includes at least one thermoplastresin, the curable composition provides elevated levels of thermoplastpolymer whereby the thermoplastic resin is present in a first amount influid phase as a matrix component and additionally is present in asecond amount in the form of at least one flexible polymer element insolid phase.

Preferably the thermoplastic resin component comprises at least onethermoplastic polymer and may be a blend of thermoplastic polymers infirst or second amounts or the same or different thermoplastic polymerin first and second amount.

The thermoplastic resin component may be present in any suitableamounts. Preferably the thermoplastic resin component is present infirst fluid phase amount of from 1 wt % up to that amount which it ispossible to blend with the matrix resin and/or impregnate into thereinforcing fibres, preferably from 1 wt % to 15 wt %, more preferablyfrom 5 wt % to 12.5 wt %; and is present in second solid phase amount offrom 1 wt % up to any desired amount which is suitable for the desiredpurpose, preferably from 1 wt % to 50 wt %, more preferably from 5 wt %to 30 wt %, most preferably from 5 wt % to 20 wt %. Accordingly thecomposition of the invention may comprise the thermoplastic resincomponent in a total amount of from 2 wt % to 65 wt % of thecomposition.

The surprising nature of this embodiment of the present inventionderives from the fact that we have found that it is possible to provideelevated levels of a thermoplastic resin component or the like in acomposition by providing a part thereof in the form of a flexiblepolymer element such as a fibre, film or the like which is capable ofdissolving in a resin matrix, whereby it may be uniformly andcontrollably combined in a curable composition and uniformly dispersedby means of at least partial phase transition as herein before definedto provide a polymer blend having desired properties.

It is moreover surprising that such polymer elements which we havepreviously found capable of undergoing phase transition in athermosetting resin matrix are capable of undergoing phase transition ina thermoplast-containing resin matrix, specifically athermoplast-thermoset resin matrix. It is moreover surprising thatcomposites comprising elevated levels of a thermoplast resin componentobtained in this manner exhibit enhanced properties as a result of theelevated thermoplast content.

A curing agent is suitably selected from any known thermoset curingagents, for example epoxy curing agents, as disclosed in EP-A-0 311 349,EPA 91310167.1, EP-A-0 365 168 or in PCT/GB95/01303, which areincorporated herein by reference, such as an amino compound having amolecular weight up to 500 per amino group, for example an aromaticamine or a guanidine derivative. Particular examples are 3,3′- and4-,4′-diaminodiphenylsulphone, (available as “DDS” from commercialsources),methylenedianiline,bis(4-amino-3,5-dimethylphenyl)-1,4diisopropylbenzene(available as EPON 1062 from Shell Chemical Co);bis(4-aminophenyl)-1,4-diisopropylbenzene (available as EPON 1061 fromShell Chemical Co); 4-chlorophenyl-N,N-dimethyl-urea, eg Monuron;3,4-dichlorophenyl-N,N-dimethyl-urea, eg Diuron and dicyanodiamide(available as “Amicure CG 1200 from Pacific Anchor Chemical). Otherstandard epoxy curing agents such as aliphatic diamines, amides,carboxylic acid anhydrides, carboxylic acids and phenols can be used ifdesired. If a novolak phenolic resin is used as the main thermosetcomponent a formaldehyde generator such as hexamethylenetetraamine (HMT)is typically used as a curing agent.

In a preferred embodiment of the invention the flexible polymer elementcomprises a polyaromatic polymer and the curable compositionadditionally comprises a catalyst for the polyaromatic polymer. In thiscase, the curing catalyst employed preferably comprises a Lewis acidhaving amine functionality, instead of in addition to conventionalcatalysts, as described in copending GB 0002145.1, the contents of whichare incorporated herein by reference. Preferably the catalyst is of theformula:LXn.R

Where LXn is a Lewis acid and R is an amine. Preferably L is selectedfrom Groups IIb, IIIb, VIII of the Periodic Table of the Elements and Xis halo.

Preferred catalysts include BF₃, AlF₃, FeF₃, ZnF₂ as Lewis acidcomponent and primary or secondary aliphatic or aromatic amine such asmonoethyl amine (mea), dimethylamine (dma), benzylamine (bea) orpiperidine.

In a further aspect of the invention there is provided a process for thepreparation of a curable composition as hereinbefore defined as known inthe art comprising contacting a flexible polymer element or a supportstructure or carrier as hereinbefore defined with resin matrix forexample by interleaving impregnating, injecting or infusing, mixing andthe like.

The composition may then be laid up with other component parts such asreinforcing fibres to provide the curable composition, or othercomposite parts such as metal or polymer or other bodies or structuresprior to curing in known manner.

Particular applications in which the flexible polymer element of theinvention as hereinbefore defined finds application are now described asnon-limiting example.

Curable compositions of this present invention find utility in producingfabrics which can be composed of a combination of the polymer derivedfrom the flexible polymer element with other resin matrix polymers, suchas high molecular weight polyesters, polyamides, e.g. nylons, etc. whichare used to form ‘scrims’ typical of the composite industry. These‘scrims’ are not complete films but possess open weave structures and assuch can be used to act as carriers for adhesive resin components. Thecombination of ‘scrim’ and resin components are then referred to asadhesive films. Such films can be used to bond composite structurestogether as well as composite to metallic structures. The flexiblepolymer element, such as soluble fibres, as part of the ‘scrim’ willdissolve as the adhesive cures and then phase separate to produce thepredetermined morphology of choice. This will improve the adhesionproperties of the resin to the substrate surfaces as well as increasethe cohesive properties of the resin. Appropriate choice of the flexiblepolymer element may also lead to improvements in environmentalresistance of the adhesive bond.

Another utility for these so called ‘scrims’ can be found as interleavesfor introducing thermoplastics into the interlaminar region ofconventional prepregs. The scrims can also be utilised in dry preformswhere the open weave structure allows the injection/infusion of thethermosetting resins to occur throughout the preform. This is unlike theinclusion of continuous films which act as obstructions to the resinflow which in turn can lead to porosity and poor mechanical andenvironmental performance.

The present invention also finds utility in the area of mouldingmaterials in which the flexible polymer element(s) can be added to amoulding compound formulation in the form of chopped fibres. The fibresare designed to remain intact, i.e. insoluble as the moulding compoundtravels through an injection moulding machine. This means that theviscosity of the moulding compound will in general be lower and willrequire lower temperatures and pressures in order to process themoulding resin. It can also mean that other additives, such as fillersand flame retardants can be added to the resin without too detrimentaleffect upon the moulding compound's viscosity.

Another utility for this invention is in the area of continuous resinfilms. Soluble fibres can be in a continuous or discontinuous form andadmixed with a range of thermoset resins in order to disperse thefibres. Such film products can then be used and applied to the surfaceor between layers of the main structural reinforcement.

Another utility for this invention is in production of continuous filmsof pure polymer which can either be used as made or further modified tosuit a particular application.

The soluble fibres and any reinforcing fibres used in the invention areincorporated with the resin matrix at any suitable stage in the process.

A curable composition comprising matrix resin optionally containing somevolatile solvent can be contacted with the flexible element by a varietyof techniques, including impregnation, injection, infusion and the like.A flexible polymer film may be foamed by solvent flashing, withsubsequent impregnation to form a composite film, for example carryingan adhesive resin, or multilaminar films may be provided using knowntechniques.

Injection may be at ambient or elevated temperature less than thedissolution temperature as known in the art, suitably in the range roomtemperature to 100 C, preferably room temperature to 75 C to confersuitable resin viscosity. Injection may be in known prepreg or preformmanner with use of a bag, mandrel and/or mould and optionally with useof channels or the like to assist flow as known in the art. Injectiontimes are suitably in the range 2 to 300 minutes, preferably 2 to 120minutes for example 2 to 30 minutes.

Preferably a fibre-reinforced composition is made by passing essentiallycontinuous fibre into contact with such resin composition. The resultingimpregnated fibrous reinforcing agent may be used alone or together withother materials, for example a further quantity of the same or adifferent polymer or resin precursor or mixture, to form a shapedarticle. This technique is described in more detail in EP-A-56703,102158 and 102159.

A further procedure comprises forming incompletely cured matrix resincomposition into film by for example compression moulding, extrusion,melt-casting or belt-casting, laminating such films to fibrousreinforcing agent and thermoplastic fibres in the form of for example anon-woven mat of relatively short fibres, a woven cloth or essentiallycontinuous fibre in conditions of temperature and pressure sufficient tocause the mixture to flow and impregnate the fibres and curing theresulting laminate.

Plies of impregnated fibrous reinforcing agent, especially as made bythe procedure of one or more of EP-A 56703, 102158, 102159 whichadditionally contain thermoplastic fibres can be laminated together byheat and pressure, for example by autoclave, vacuum or compressionmoulding or by heated rollers, at a temperature above the curingtemperature of the thermosetting resin or, if curing has already takenplace, above the glass transition temperature of the mixture,conveniently at least 180° C. and typically up to 200° C., and at apressure in particular in excess of 1 bar, preferably in the range of1–10 bar.

The resulting multi-ply laminate may be anisotropic in which the fibresare continuous and unidirectional, orientated essentially parallel toone another, or quasi-isotropic in each ply of which the fibres areorientated at an angle, conveniently 45° as in most quasi-isotropiclaminates but possibly for example 30° or 60° or 90° or intermediately,to those in the plies above and below. Orientations intermediate betweenanisotropic and quasi-isotropic, and combination laminates, may be used.Suitable laminates contain at least 4 preferably at least 8, plies. Thenumber of plies is dependent on the application for the laminate, forexample the strength required, and laminates containing 32 or even more,for example several hundred, plies may be desirable. Woven fibres are anexample of quasi-isotropic or intermediate between anisotropic andquasi-isotropic.

Alternatively or additionally the laminate may be single or multiply,and include directional strengthening with one or more over laidstrengthening fibres, stitched in place with the soluble fibre (TFP).Laminates may be assembled in shaped manner, for example 2 fabrics maybe oriented at right angles to each other to form struts and the like,and stitched in place with soluble fibre.

Preferably a curable composition provided according to the invention isa liquid moulded composition obtained by a liquid moulding method asknown in the art wherein a flexible polymer element or a supportstructure or carrier as hereinbefore defined comprising reinforcingfibres (dry) and the at least one flexible polymer element is placedinto a bag, mould or tool to provide a preform and matrix resin isinjected/infused directly into the combined fibres and element.

In a further aspect of the invention there is provided a method for thecuring of a curable composition comprising providing the composition ashereinbefore defined, providing additional components including otherreinforcing matrix components, additives and the like, subjecting toelevated temperature for a period suitable for phase transition offlexible polymer element, and subjecting to further elevated temperaturefor a period suitable for gelling and/or curing of curable component,and the curing thereof to provide a cured composite.

Additional fibre reinforcement or resin matrix may be incorporated withthe support structure prior to curing thereof.

The preform is preferably formed, injected/infused and cured byprocessing techniques such as Resin Transfer Moulding (RTM), LiquidResin Infusion (LRI), Resin Infusion Flexible Tooling (RIFT), VacuumAssisted Resin Transfer Moulding (VARTM), Resin Film Infusion (RFI) andthe like as hereinbefore referred.

Suitably the process includes a preliminary stage of infusion ofadditional resin matrix at reduced pressure, followed by a degassingstage drawing off air for reducing voidage. Traditionally the degassingis carried out under elevated pressure.

In a particular advantage of the invention however we have found thatdegassing may be carried out at ambient or reduced pressure without voidformation with use of a particular support structure or carrierconfiguration as hereinbefore defined wherein fibres of two differentdiameters are laid up in coaligned arrangement creating channelstherebetween, which assists air flow. In this case the panel may beinfused, degassed and cured using RIFT or VARTM techniques such asvacuum bagging, without the need for an external pressure from anautoclave to apply to the bag surface.

In this case the support structure or carrier comprises aligned soluble,and optionally additionally structural, fibres of two distinct averagediameters. Suitably the support structure or carrier comprises thereforea multiaxial fabric in which fibres of a first diameter which may besoluble or structural, are laid up in colinear arrangement with fibresof greater diameter, coaligned along the first fibres, thereby creatinglongitudinal channels throughout the composition.

The first fibres are usually structural fibres, but optionally theembodiment of this invention comprises a support structure or carrierhaving soluble fibres of two diameters, whereby channels are createdtherebetween, some or all fibres dissolving on curing to give acomposite or neat resin panel of 0% voidage.

We have suprisingly found that in the support structure or carrier ofthis embodiment, the fibre form flexible polymer elements remain infibre form in the initial stages of degassing, at ambient or reducedpressure and draw air off from the panel whereafter the fibres dissolveand disperse without trace allowing the fluid phase components tocompact, without external applied pressure, prior to onset of gellingand curing. If external pressure is applied the performance is simplyenhanced, however it is a particular advantage that this configurationallows for the first time curing large panels without the need for anautoclave or the like.

Suitably soluble fibres are present in an amount of 2 to 50 wt %,preferably 2 to 40 wt %, more preferably 4 to 16 wt % in thisembodiment. Suitably the soluble fibre is present as multifilament ofTex 30–160, laid up against structural fibre of diameter 5 to 10 microneg 6 or 7 micron.

Additionally the configuration has advantages during the resin infusionstage, whereby channels assist in rapid and uniform infusion throughoutthe panel.

In a further advantage this configuration provides improved infusionwith excellent control of the resin flow front.

Suitably the process of the invention comprises subjecting to elevatedtemperature in the range up to 300° C. for example 60 to 200 C, morepreferably 75 to 150 C for a period of up to 45 minutes, preferably 0.5to 35 minutes to effect phase transition. Temperatures in the range100–150° C. are particularly suitable for phase transition of readilysoluble flexible polymer elements for example of low MW, present inreadily soluble concentration in an effective curable component solvent,and in the range 150° C. to 300° C. for less readily soluble flexiblepolymer elements. Suitable elevated temperature is selected in a desiredrange to effect phase transition in a desired time, for example a givenflexible polymer element may be subjected to elevated temperature in therange 135 to 170° C. for 2–10 minutes, 125 to 135° C. for 5–30 minutesor 105 to 125° C. for 10–40 minutes.

Phase transition may be at ambient or elevated pressure corresponding tothe desired injection, degassing and curing conditions.

The process includes subjecting to further elevated temperature afterphase transition to cause onset of gelling or curing. Gelling may be attemperature in the range corresponding to pre cure in known manner.Gelling is preferably followed by further elevated temperature cure, orthe gelled composition may be cooled for later curing, for example ifgel or cure is in an autoclave, or mould, the composition may be removedfrom the autoclave or mould and cure continued at ambient pressure inregular oven.

Gelling or curing is suitably carried out by known means as elevatedtemperature and pressure for a suitable period, including temperatureramping and hold as desired. A suitable gelling or cure cyclecorresponds to that for a conventional composition comprising the samecomponent types and amounts and reference is made to the description andexample illustrating calculation of amount of flexible polymer elementpresent in the composition.

Preferably cure is at temperature in the range 180 to 400° C. for 1–4hours, for example. Additionally the process may include post curing atsuitable conditions to enhance properties such as Tg and the like.

Gelling or curing may be with use of catalysts as hereinbefore defined,whereby temperature increase causes activation, and cooling belowactivation temperature halts curing.

The process may be monitored in real time but preferably a suitablereaction time and temperature is predetermined for a given composition,for example by preparing samples and analysing solution and dispersionafter completion of gelling or cure, for example by use of Ramanspectroscopy or the like.

In a further aspect of the invention there is provided a kit of partscomprising a flexible polymer element as hereinbefore defined, asolution pair resin matrix suitable for dissolving the flexible element,and optional reinforcing fibre as a support structure or carrier or asseparate components, together with any additional reinforcing fibres,matrix, monomers or polymers, curing agents and the like.

In a further aspect of the invention there is provided a cured compositeor resin body comprising cured matrix resin and optional structuralfibres, and dispersed cured polymer derived from soluble flexiblepolymer elements as hereinbefore defined, in common phase or phaseseparated from the matrix resin.

In a further aspect of the invention there is provided a method forselecting or blending a resin matrix suitable for assisting indissolving a flexible polymer element as hereinbefore defined, withreference to class, molecular type, and the like. The higher themolecular weight of the polymer the greater the compatibility orsolution effect needed from a solution pair resin matrix, for examplepolyfunctional epoxies are more effective than mono or difunctional, andphenolics more effective than cyanate esters or BMI.

In a further aspect of the invention there is provided a complex shapedstructure prepared without use of a mould, comprising assembled sectionsin which flexible polymer element is used as hereinbefore defined aswoven and/or stitching to confer mechanical properties and/or to conferplanarity, fold seams, reinforcing for hinges and bolt holes,directional strengthening and the like and for assembly, and sectionsare assembled with use of flexible polymer element as stitching to holdthe structure in place during resin injection. Particular structureswhich may be provided include net shape preforms and assembled panelsfor use in aerospace, automotive, marine, wind energy and likeapplications.

In a further aspect of the invention there is provided a flexiblepolymer element, support structure or carrier, prepreg or preform,curable composition or cured composite or resin body as hereinbeforedefined for use in the preparation of an engineering composite, inaerospace, automotive, marine, wind energy, industrial application, insporting goods and papermills, as an adhesive, functional or protectivecoating for example for rollers, sheet metal, electrical insulation andthe like, in particular as stitched fabric for example in constructingautomotive body parts, reinforced films such as monofilm, forreinforcing or filament overwinding in preparation of pipes, tanks,rollers or in reinforcing engineering structures such as bridges and thelike.

The invention is now illustrated with reference to the following Figureswherein

FIG. B1 (see hereinbefore) shows figuratively the Dissolution of fibreand Phase Separation;

FIG. B1 a shows dissolution time for fibres at different temperaturesfor compositions according to the invention including different matrixepoxy resin components and different catalytic components

FIG. B1 b shows curves for dissolution time and gel time at differenttemperatures, showing a greater delta time (gel minus dissolution) attemperature of ca. 120 C. than 140 C, the delta time allows for alloriginal tensions and residual stresses to disappear before resin gel

FIGS. B2 b to B2 d show Raman spectra for a cured composition (ofcomposition shown in FIG. B2 a) of the invention showing uniformdispersion of dissolved fibres in epoxy resin matrix

FIGS. B3 a and B3 b show mechanical properties of fibres

FIG. B4 (see hereinbefore) shows figuratively typical two phasemorphologies of thermoplast/thermoset systems;

FIG. D1 shows a woven carbon and soluble fibre configuration

FIGS. D2 to D6 and D7 a to D7 c show configurations of multiaxialconfigurations and of stitching and weaving types as hereinbeforedescribed

FIGS. E1 a to E1 c show dissolution of polymer fibre stitching of theinvention compared with insoluble polyester stitches, in multiaxialfabrics using the same style/weight stitched with polyester and solublefibre, in alternate layers

FIGS. E2 a to E2 c show hybrid woven fabric of C warp vs C and solublepolymer weft and SEM pictures of the fabric at different temperaturesillustrating undissolved fibre at the outset and subsequent completedissolution of fibres in the matrix

FIG. F4 a shows influence of polyaromatic concentration on thedissolution time of the polyaromatic fibre in polyaromatic/epoxycomposition for a fabric as shown in FIG. 2.

FIG. G2 shows processing equipment used and FIGS. G2 a to G2 d showpanels prepared with soluble fibre co-aligned with structural fibre oflesser diameter, and processed at ambient pressure showing zero voidformation by air draw off though channels created by dissimilar diameterfibre alignment, together with comparisons showing void formation inpanels lacking the soluble fibre.

The invention is now illustrated in non-limiting manner with referenceto the following Examples wherein

Section A—Soluble Fibres for a Support Structure or Carrier

EXAMPLE A1

Preparation of Fibres

In the Examples the following polymers listed as Table I were employedfor preparing flexible polymer elements of the invention:

Polymer Molecular Weight End Groups 40:60 PES:PEES 9,000 Amine 40:60PES:PEES 12,000 Amine 40:60 PES:PEES 15,000 Amine 40:60 PES:PEES 12,000Hydroxyl 40:60 PES:PEES 7,000 Chlorine 40:60 PES:PEES 9,000 Chlorine40:60 PES:PEES 15,000 Chlorine 100% PES (Sumitomo 24,000 Hydroxyl 5003P)

Additionally the following polymers listed as Table Comparative I wereemployed for preparing insoluble fibres not according to the invention:

Polymer Molecular weight End Groups 100% PEEK 15,000 Fluorine PolyesterPES Polyester TRIVERA

Polymers are commercially available or may be prepared as described inEP 311349, WO 99/43731, GB 000 2145.1 or GB 0020620.1 the contents ofwhich are incorporated herein by reference.

In the following examples fibres are produced both in the laboratory andalso on a commercial extruder.

EXAMPLE A2

Spinning of the Polymers Into Fibres Using a Laboratory Scale Extruder

This was carried out using a 15 cm³ micro-extruder, series No 98013, asmanufactured by DSM.

The polymer resins were melted using a range of temperatures and thequality of the fibres was assessed by their draw ability, aestheticqualities and their toughness/flexibility. This property was determinedinitially by simply observing the ability of the fibre to be knottedwithout breaking. In the case of the 40:60 PES:PEES copolymers thetemperature range which was studied varied from 270° C. up to 320° C.

The polymers detailed in the Table were all evaluated in thistemperature range and it was found that a melt temperature of 290° C.gave the best quality fibre from the hot melt extrusion. However, thiswas only the case for the series of 40:60 PES:PEES copolymers. In thecase of the 100% PES a minimum melt temperature of 320° C. was required.However, temperatures as high as 350° C. were required in order toreduce melt strength and be able to draw thin fibres.

EXAMPLE A3

Spinning of the Polymers Into Fibres According to the Invention Using anIndustrial Scale Extruder

In order for this to be successfully carried out on an industrial scaleit was important that the polymer powders were converted into pellets.This was achieved using a twin screw extruder with three dies of 35 mm,a length of 1400 mm and 10 temperature zones. The following temperatureprofile was used:

Zone Temperature (C.) Feeding 1 Rt-100° C. Extrusion 1 Extrusion 2increasing Extrusion 3 {close oversize brace} 250–375 Extrusion 4Extrusion n Head 1 steady Head 2 250–375 Head 3 {close oversize brace}Head n

The screw speed was 230 rpm and the T melt of the polymer was 294 C. Theextruded polymer was water cooled at RT and dragged into a chopper. Theaverage diameter of the pellets was 3 mm.

The pellets were then transferred to a single screw extruder with a Diediameter of 45 mm and a length of 1.26 meters. The following temperatureprofile was used:

Zone Temperature (C.) Extrusion 1 Extrusion 2 increasing Extrusion 3{close oversize brace} 250–375 Extrusion n Head 1 Head 2 {close oversizebrace} steady Pump 1 250–375

The temperature of the melt polymer was 295 C. Pump speed was set togive a desired Tex and desired tenacity at break. Four different Texfibres of the invention in the range 30 to 60 Tex were obtained withdifferent pump speeds. The minimum screw speed was set at 11 rpm and thefollowing machine parameters were chosen to give a mono filaments fibrediameter of 30 microns:

Spinning die head diameter × holes 0.3 mm × 100 Quench bath temperature60 C. 1^(st) Stretching unit speed Not used 1st orientation oventemperature 25 C. 2^(nd) stretching unit speed 200 m/min 2^(nd)orientation oven temperature 25 C. 3^(rd) stretching unit speed 200m/min 3^(rd) oven temperature 25 C. 4^(th) stretching unit speed 200m/min

Fibres were pulled in air for a distance of 50 to 500 mm, according todesired modulus.

3.1 Optimisation of Drawing Temperature for Various Polymers.

In the case of the 40:60 PES:PEES Copolymers the temperature range whichwas studied varied from 250 C up to 375 C. The polymers detailed inTable 1 were all evaluated in this temperature range and an optimum melttemperature was selected that gave the best quality fibre from both hotmelt extrusion and the melt flow indicator. The optimum melt temperaturefor the series of 40:60 PES:PEES copolymers was different to that forthe 100% PES, for which a higher minimum melt temperature was required,and higher temperatures were required in order to reduce melt strengthand be able to draw thin fibres.

EXAMPLE A4

Outlife of PES:PEES Polymers Under Hot Melt Extrusion Conditions

Samples of the amine ended 40:60 PES:PEES, 9K were studied using an RDSRheometer with parallel plates. A sample of the polymer was heated upto290° C. and held isothermally for over 3 hours. During this time therewas very little change to the rheological properties of the resin. Thiswas confirmed by NMR evaluation of the polymer before and after heating.The NMR showed no change to the molecular weight and number of endgroups on the polymer.

Flexible polymer elements or support structures or carriers of theinvention can therefore be stored at ambient or elevated temperature forextended periods up to years without dissolution, and only on contactingwith solvent does the element dissolve in the order of minutes up todays.

EXAMPLE A5

Mechanical Properties of Fibres

All of the fibres studied in this programme were characterised to assessthe fibres Modulus, Strength, Toughness and % Elongation. An InstronUniversal Testing Machine model 5544 was used to carry out these tests.The Instron was fitted with a 5N tension/compression load cell. A gaugelength of 100 mm was used for each specimen and a test speed of 50mm/min. Measurements were made in a controlled laboratory environment,with a temperature of 23° C. and a relative humidity of 50%.

A minimum of 10–15 specimens per material were tested.

A number of properties were derived from the mechanical evaluation ofthe fibres these were:

-   -   1. Stiffness via Tensile Modulus    -   2. Strength via Maximum Tensile Stress (used to calculate D Tex)    -   3. Toughness via Energy to Failure    -   4. Displacement or % Elongation

In addition, flexibility is observed. Flexibility is empirical and isinversely proportional to diameter, and is a function of modulus

The following Table details the results of the mechanical behaviour of arange of thermoplastic fibres as manufactured under Example 1(laboratory extruder).

Polymer Maxi- Energy to Fibre % mum Failure/ Polymer MW/end Elon- Stressunit area U/ Modulus Fibre Type groups gation (Mpa) mJ/mm³ (Gpa)PES:PEES 7 K 27 42 929 1.44 40:60 Chlorine ended PES:PEES 15 K 48 1715764 3.29 40:60 Chlorine ended PES:PEES 9 K 55 104 4451 5.01 40:60 Amineended PES:PEES 12 K 52 93 3088 4.81 40:60 Amine ended PES:PEES 15 K 5598 4164 4.3 40:60 Amine ended PES 24 K OH 30 116 2627 4.5 ended

From the table it will be apparent that flexible elements may beselected by polymer type to provide desired properties for stitching,weaving, comingling or other desired support or carrier function, withreference to their inherent properties.

It should be noted that all the fibres in the above Table were producedon a laboratory extruder and as such the results should be viewed asbeing approximate and some results may be effected by the quality of thefibres.

EXAMPLE A6

Comparison of Other Fibre Types not According to the Invention

The following Table details the mechanical test results of alternativefibres to those based on 40:60 PES:PEES copolymers.

Energy to Maximum Failure/unit % Stress area U Modulus Polymer FibreElongation (Mpa) (mJ/mm³) (Gpa) 100% PEEK 116 110 8674 2.07 Polyester(trade 33 24 — 0.2 name PES) Polyester (trade 36 15 — 0.13 name TRIVERA)

PES and TRIVERA are both typical examples of commercial multi-filamentpolyester stitch used to stitch carbon fibre fabrics. It should be notedthat all other fibres studied are examples of single mono filamentfibres.

Section B—Support Structure or Carrier Comprising Soluble Fibre andDissolving Matrix Resin

EXAMPLE B1

Solubility of the Fibres in Epoxy Resin

This was carried out using a hot stage microscope. A single fibre wasplaced between two microscope slides and an epoxy resin was introduced.The slide was placed into the hot stage of the microscope and thematerial was heated from RT up to 180° C. at a rate of 2 C/min. Thedissolution properties of the fibre was followed and recorded.

Study of amine ended 40:60 PES:PEES, 9K solubilised in Araldite PY306(Ciba Geigy) epoxy resin as a function of temperature revealed thatthere was polymer dissolution even at temperatures as low as 90 to 100°C. As the temperature continued to rise so did the solubilising natureof the polymer fibre. Finally at 180° C. the fibre could not be seen anymore and had completely dissolved.

These observations are very important as the fibre itself should not beto soluble at low injection temperatures. If they were then it ispossible that as the flow front of the resin, from the injectionprocess, proceeds from one side of the injection port to the exit portit could carry dissolved polymer fibre which would exit the LM tool. Thepolymer fibres solubility was in fact such that it remained dormantuntil the initial injection/infusion of the resin had been completed andthe moulds injection/infusion and exit ports had been closed. After thisthe fibre then slowly dissolved as the temperature of the LM mould wasincreased to the final cure temperature.

At this point the polymer dissolved and entered into the reaction of thethermoset cure finally to phase separate and toughen the LM compositepart.

Study of amine ended 40:60 PES:PEES, 9K solubilised in MY 0510 epoxyresin as a function of temperature revealed once again that the polymerfibre in this particular epoxy was seen to be solubilising attemperatures as low as 70 to 80° C., and in MY721 at temperatures of 110to 120 C.

The same PES:PEES systems were investigated without DDS curing agent.There was none or negligible difference with MY epoxies, but an increasein dissolving temperature with PY epoxy.

FIG. B1 shows figuratively the dissolution process, derived fromphotographic images.

FIGS. B1 a and B1 b show time temperature curves for dissolution offibres in epoxy resin, for different formulations, and also showing thetime to dissolution and time to gel at different temperatures,indicating that very fine control of solution and of gelling onset canbe provided by the present invention ensuring complete fibre dissolutionbefore onset of gelling.

EXAMPLE B2

Dispersion of Soluble Fibre in Matrix Resin and Mechanical Testing

FIG. B2 a shows the preparation of panels for mechanical testing anddiffusion studies through Raman.

FIGS. B2 b to B2 d show Raman spectra of the cured composite. Themicroscope was focussed at different points on the resin block, severalnm apart, just below the surface.

Using a Raman 800 μm pinhole, 633 nm laser, the microscope was focusedat different points on the polished resin panel (several mm apart).

The most suitable wavenumber shift peak to identify the polysulphonepolymer from the soluble fibre is at 790 cm-1: this peak shows asignificant signal/noise ration with the less possible overlapping witha peak of the neat matrix resin.

In the analysis we monitored the relative intensity of the 790 cm-1 bandcompared with the surrounding peaks. The band remained at a very similarintensity when compared with the other features. Even in 20 differentareas spectral shapes overlay very well—this confirms the dissolutionand uniformity of the Soluble fibre polymer in the thermoset resinmatrix.

FIG. B2 d shows spectra in the 740–880 region on 20 different points andillustrates that these are very precisely superimposable, indicatinguniform concentration of polysulphone at each point.

EXAMPLE B3

Mechanical Tests on Neat Resins From Soluble Fibres and Matrix Resin

Tests were conducted on several panels prepared with different level ofsoluble fibres.

The fracture toughness in terms of energy G_(c) and the fracturetoughness in terms of strength K_(c) are the same

The very low standard deviations in the mechanical test results (around5%) indicate a very good diffusion of the thermoplastic modifier afterdissolution

The other properties measured (Modulus in flexure, yield strength intension and Tg) are also the same

FIGS. B3 a and b show energy and strength fracture toughness, theresults are almost identical, in each case the system with solublefibres showing higher Gc and Kc at thermoplastic content <10% and >17%.

Compression, tension, compression after impact (CIA), in plane shearstrength (IPS) were tested on panels and values were comparable withcommercial panels and showed good uniformity with no delamination. Openhole tension, G1 c and G2 c are expected to be comparable.

EXAMPLE B4

Morphology Study

The following resin formulation containing MY0510, manufactured by ShellChemicals, PY306, manufactured by Ciba Geigy, MDEA, manufactured byLonza Chemicals and Chopped fibres of amine ended 40:60 PES:PEES, 9Kwere mixed and degassed at about 90° C. prior to being cured at 170° C.for 3 hours. Samples of the cured panels were polished and etched andexamined by Scanning Electron Microscopy (SEM). The following resinformulation's were prepared using 15, 22.5 and 30% of the choppedfibres:

Resin Formulation A/ Formulation B/ Formulation C/ Component % % %MY0510 25.03 22.08 20.6 MY721 PY306 26.27 23.23 21.7 MDEA 24.82 21.920.44 Amine ended 15 22.5 30 40:60 PES:PEES, 9K fibres

Typical morphologies are shown in FIG. B4.

EXAMPLE B5

Solubility in Alternative Matrix Resin

Polysulphone fibre was dissolved in L10 cyanate ester having viscositycomparable to water. Injection was therefore very favorable. L10 has ahigher dissolving power than epoxy because it is of lower viscosity. Itis also more compatible with the polysulphone.

Fibres were found to dissolve at temperatures of 100, 110, 120, 130 and140 C with time decreasing from 20 to 3 minutes.

The fibre was then dissolved in a blend of L10 and epoxy MY0510 toconfer phase separation. The resin still injected well, cyanate esterlowering the blend viscosity, and the epoxy conferred the desired phaseseparation.

Section C—Support Structure or Carrier Comprising Soluble Fibre and 2Component Resin Matrix (Thermoset and Thermoplast Polymer)

EXAMPLE C1

Morphology Study of Cured Resin

Micrographs were produced from a hot stage microscope, which follows thedissolution of a single PES:PEES fibre dispersed in a 40:60PES:PEES/epoxy resin, the PES:PEES content was about 10 to 15%. Afterdissolution the field of view was adjusted to look at the bulk sample.After 30 minutes at 175° C. a noticeable particulate phase separationwas observed.

Section D—Support Structure or Carrier Comprising Soluble Fibre andStructural Fibre: Configurations

EXAMPLE D1

Multiaxial Fabrics Configuration

The different uses of multiaxial fibre showing incorporation along thestructural fibres and use as stitching thread are shown in FIG. D1

EXAMPLE D2

Use of Soluble Fibres as Stitching Thread in Non Crimp Fabrics

Soluble thread is stitched into carbon fibres as non crimped fabric inknown manner as shown in FIG. D2. When used in a curable composition thestitches dissolve giving a smooth non-crimped finish.

EXAMPLE D3

Tailored Fibre Placement (TFP

Fibres were used as upper and lower thread, with stitching speed ofaround 1200 stitches/min. Fibres were placed along the structural Cfibres, and were also placed around circular and rectangular cut outsetc. Configurations are shown in FIG. D3.

EXAMPLE D4

Assembly of Fabrics and Preform Construction

FIG. D4 shows a preform having several fabrics coassembled

EXAMPLE D5

Stiffening of Woven Fabrics Using Soluble Fibre

FIG. D5 shows a panel in which cross stitching is placed to stiffen alow weight 5 harness satin fabric in order to stabilise it whensubjected to shear during handling.

EXAMPLE D6

Use of Soluble Fibres Stitch as Folding Seams For Preforms

FIG. D6 shows a panel which is stitched to form seams for folding inpreform shaping and assembly

EXAMPLE D7

Hybrid Fabrics

FIGS. D7 a to c show hybrid woven fabrics of carbon fibre with PES:PEESyarn.

Section E—Support Structure or Carrier Comprising Soluble and StructuralFibres and Matrix Resin

EXAMPLE E1

Comparison of Fibres Performance

FIGS. E1 a–c show solubility of soluble PES:PEES stitching compared topolyester stitching in multiaxial fabrics. Panels were made using thesame fabric style/weight stitched with polyester and PES:PEES 60 Texfibres and alternating the layers (one with polyester stitch, one withPES:PEES stitch etc). The panels were subjected to elevated temperatureof 125 C with hold for dissolution to take place.

In the figures the PES:PEES fibre has dissolved without trace but thepolyester stitching is still visible.

EXAMPLE E2

Comparison or Fibres Solubility at Different Temperature

FIGS. E2 a and E2 b show dissolution by SEM taken through cross sectionsof lamina of 10 plies laid up in [0,90] configuration, each lamina beingyarns or polysulphone fibre cowoven in weft direction on both sides of aC tow, injected with epoxy resin and cured with hold at differenttemperatures then post cured. Hold at 105 C shows incomplete dissolutionwhereas at 135 C the fibre is completely dissolved without visibletrace.

Section F—Support Structure or Carrier Comprising Soluble and StructuralFibre and 2 Component Resin Matrix (Thermoset and Thermoplast)

EXAMPLE F1

Controlling Amount of Fibres in a Support Structure or Carrier

An amount of continuous, chopped or woven soluble fibres may bepre-weighed and laid up in desired manner with structural fibres and/ormatrix according to the invention, providing a desired amount of polymerderived from the soluble fibres.

The present example illustrates calculation of fibre incorporation inthe case of stitching or weaving structural fibres as hereinbeforedefined, to ensure desired total amount of soluble fibre form flexiblepolymer element.

A curable composition comprising coweave or polysulphone fibre andstructural fibre is prepared. The resultant cured composite is requiredto comprise 35% matrix resin comprising epoxy resin and PES:PEES resintogether with 65% structural carbon fibre. These proportions aredistributed in the curable composition to comprise 25% matrix resincomprising the same amount of epoxy and 10 wt % less of PES:PEES,together with 75 wt % of structural carbon and PES:PEES soluble fibre,in proportion 65:10 which corresponds to percentage 100:16.

The structural carbon is to be laid up with Tex_(sf) (weight structuralcarbon fibre in grams of 1000 m carbon)=800.

From the formula Tex_(fpe)=(% wt_(sf)×% wt_(fpe))÷Tex_(sf)Tex_(fpe)=100×16÷800=2

From this calculation the parameter (tows/cm) of the weaving machine isset to provide the desired Tex_(fpe) as calculated.

EXAMPLE F2

Impregnation of Support Structure or Carrier With Curable Component

In the Examples the polymers listed in Table AI above were employed.

The epoxy or epoxies, in amount shown in Table FII were warmed, attemperature not exceeding 60° C. 40:60 PES:PEES copolymer with primaryamine termination, 12K, was synthesised by reacting 1 mol of DCDPS with2 moles of m-aminophenol using potassium carbonate as the catalyst andsulpholane as the reaction solvent. The polyaromatic, dissolved in asmall amount of dichloromethane, was then added in corresponding amountshown in Table FII. Once the resins had been warmed and their viscosityreduced the solvent was removed at 60° C. The resin was used immediatelyor cooled for later use.

A mesh of reinforcing fibre and polysulphone fibre obtained by themethod of Examples above, in respective amounts shown in Table FII wasimpregnated with the resin to give a total composition having thecontent

TABLE FII RESIN PART A Epoxies and curing agent 17.5% PART B1Predissolved polysulphone 10.5% REINFORCEMENT PART B2 Polysulphonefibres   7% PART C Carbon   65%

A hybrid textile reinforcement configuration, for example woven fabricor a multiaxial fabric was used eg as illustrated in FIG. F2.

EXAMPLE F3

Infusion of Support Structure or Carrier With Curable Component

Infusion was carried out in known manner to thoroughly wet andimpregnate the hybrid fabric, and using the above calculated amount ofresin matrix components.

EXAMPLE F4

Cured Composite of Example F2

The composites obtained in Example F2 were subject to elevatedtemperature for dissolution of fibres, and on dissolution were subjectto further elevated temperature for curing.

FIG. F4 a shows dissolution of polysulphone fibres in the above systemwith different amounts of polysulphone (from 0 to 30%). The graph showsthat the dissolution occurs also for high level of polysulphone. Theslightly higher dissolution times for higher concentrations ofpolysulphone are due only to the higher viscosity.

EXAMPLE F5

Properties of the Composite of F4 Toughness

The use of 50% thermoplastic would cause a definite improvement inproperties like toughness.

An increase in the level of thermoplastic leads to an improvement intoughness properties like Gc and Kc as reported in the following Table.

Polysulphone % Gc (kJ/m) Kc (MPa · m½) 30% 1.36 0.61 40% 1.51 0.82 50%1.82 0.98Section G—RIFT Infusion of Laminates for Infusion and Cure Under VariedPressure or Vacuum

In conventional RTM or RFI individual prepregs are stacked in aprescribed orientation to form a laminate, The laminate is laid againsta smooth metal plate and covered with successive layers of porousteflon, bleeder fabric and vacuum bag. The autoclave pressure vesselprovides controlled heating of a mold and laminate in a pressurizedatmosphere. It applies a vacuum to the interior of the mold assemblagein order to draw off volatiles and to maintain the pressure differentialbetween inside and outside. Commonly a flexible sheet or bag covers theuncured laminate on the mould. With a vacuum applied to the laminate andpressure applied to the outer surface of the bag, a consolidatingpressure is applied to the laminate, to consolidate the individuallayers, squeeze the excess resin out compress bubbles of any volatilethat remain.

The pressurized atmosphere is commonly about 560 kPa–690 kpa (85 psi–100psi). The entire operation of the autoclave is computer controlled.

VARTM simplifies hard mold RTM by employing only one-sided moulds, andusing vacuum bagging techniques to compress the preform. Resin injectionis driven by the 1 atm pressure difference between the mould cavity andthe resin source but mould filling times can be far too long, and resindoes can cure before total fill.

RIFT provides a ‘distribution media’, being a porous layer having verylow flow resistance, provides the injected resin with a relatively easyflow path. The resin flows quickly through the distribution media, whichis placed on the top of the laminate and then flows down through thethickness of the preform.

EXAMPLE G1

Method According to the Invention Using Reduced or Ambient Pressure

The method of the invention consists of using an hybrid fabriccontaining structural fibres (carbon, glass, aramid etc) andpolysulphone multifilament having a count between 30 and 160 texcomposed of single fibres having a diameter between 30 and 80 micron asshown in the FIG. G1 a.

The structural fibres, for example carbon fibres, have usually diametersaround 6–7 micron and are therefore smaller than the above polysulphonefibres. This difference in diameter creates artificial ‘channels’ thatfacilitate the injection and also the subsequent air removal from thelaminate.

EXAMPLE G2

Samples

The following fabrics have been used to manufacture composite laminates

Aerial weight Fabric Style (gsm) Fibre in warp Fibres in Weft A 5HS 370Carbon HTA Carbon HTA 6k 6k B 5HS 370 + 59 Carbon HTA Carbon HTA 6k + 6ksoluble fibres

The fabrics have been cut in various rectangular shapes with a size of6×4 in and laid following the lay-up [0,90]8 to produce compositelaminate using a RIFT process.

FIG. G2 shows the RIFT equipment that has been used for the example. Theyellow fabric is the flow distribution media used to infuse the resin.The T connector constitutes the gate and the vent and their shapecreates a stable flow front.

Both the panels were injected and cured at temperatures in the range 75C to 180 C with suitable hold

A resin with the following formulation was injected:

% PY306 36.86 MY0510 35.42 44′DDS 27.72

The following injection times were measured: Panel A—162s, Panel B—118s.

Therefore the injection time is lower for the panel with the solublefibres. This shows that the fibres create channels that make the resininjection easier.

The SEM pictures of FIGS. G2 a and G2 b are taken from the panel A i.e.without soluble polysulphone fibres

It is possible to see big voids: they are clearly evident even undervisual observation.

FIGS. G2 c and G2 d are taken from the panel B i.e. the panelmanufactured with the hybrid carbon/polysulphone fibres:

In this case, even if the panels have been cured without pressure is notpossible to see any voids.

This method has clearly the additional advantage of not leaving anyinsoluble fibres i.e. polyester/nylon etc in the final components.

1. A support structure comprising a flexible polymer element incombination with reinforcing fibers for use in a curable compositionwith a resin matrix component wherein the flexible polymer element is amono or multi fiber or mixtures or weave thereof and is in solid phaseadapted to undergo at least partial phase transition to fluid phase oncontact with the resin matrix component of the curable composition inwhich it is soluble at a temperature which is less than the temperaturefor substantial onset of gelling or curing of the curable compositioncharacterized in that the phase transition to fluid phase is by solutionof the soluble polymer in the resin matrix component, wherein the matrixresin is curable and is selected from the group consisting of an epoxyresin, an addition-polymerisation resin, a bis-maleimide resin, aformaldehyde condensate resin, a formaldehyde-phenol resin, a cyanateresin, an isocyanate resin, a phenolic resin and mixtures of two or morethereof, wherein the flexible polymer element comprises at least onepolyarylsulphone comprising ether-linked repeating units orthioether-linked repeating units, the units being selected from thegroup consisting of-(PhAPh)_(n)-and-(Ph)_(a)- wherein A═CO or SO₂, Ph is phenylene, n=1 to 2 and can befractional, a=1 to 4 and, can be fractional and when a exceeds 1, saidphenylenes are linked linearly through a single chemical bond or adivalent group other than —CO— or —SO₂— or are fused together directlyor via a cyclic moiety, such as acid alkyl group, a (hetero) aromatic orcyclic ketone, amide, imide, imine.
 2. Support structure as claimed inclaim 1 wherein the flexible polymer element further comprises liquidrubbers having reactive groups, aggregates, metal particles, filler,pigments, nucleating agents, stabilisers, agents for increased solventresistance, flame retardants, crystalline polymers, binder, adhesives,or coating agents.
 3. Support structure as claimed in claim 1 whereinthe units of the at least one polyarylsulphone are:X Ph SO₂Ph X Ph SO₂Ph(“PES”) and  (I)X(Ph)_(a) X Ph SO₂Ph(“PEES”)  (II) where X is O or S and may differ fromunit to unit; the ratio is I to II ratio is between 10:90 and 80:20. 4.Support structure as claimed in claim 1 wherein the number averagemolecular weight of the polyarylsulphone is in the range 2000 to 25000.5. Support structure as claimed in claim 1 wherein the polyarylsulphonecontains pendant or chain-terminating groups selected from OH, NH₂, NHR′or —SH, where R′ is a hydrocarbon group containing up to 8 carbon atoms,epoxy, (meth)acrylate, cyanate, isocyanate, acetylene or ethylene, as invinyl allyl or maleimide, anhydride, oxazaline and monomers containingsaturation.
 6. Support structure as in claim 1 wherein the reinforcingfibers and the mono or multi filament fibers comprise a fabric, web,weave, non woven, overwinding, preform, scrim, mesh, fleece, roving,prepreg, composite laminar film, interleave or a mixture thereof or isstitched, sewn, or threaded.
 7. Support structure as in claim 1 whereinthe reinforcing fibres are insoluble fibers, selected from the groupconsisting of organic polymer, inorganic polymer, carbon, glass,inorganic oxide, carbide, ceramic, and metal fibers.
 8. Supportstructure as in claim 1 wherein reinforcing fibres are laid up in adesired arrangement and the flexible polymer element is in the form ofstitching, securing the reinforcing fibers arrangement, adapted toundergo phase transition in manner to disperse locally or universally inthe curable composition and to provide at least partially tracelesssoluble stitching.
 9. Support structure as claimed in claim 8 whereindesired arrangement is selected from the group consisting of random,mono or multiaxial, (co) linear or (co) planar.
 10. Support structure asin claim 8 wherein the soluble stitching is selected from tailoredfibers placement (TFP) for directional strengthening, stitching formedalong a desired fold line, stiffening stitching, assembly stitching, noncrimped fabric (NCF) stitching, and through the thickness (TTF)stitching.
 11. Process for the preparation of a support structure as inclaim 8 comprising providing at least one flexible polymer element, andproviding reinforcing fibers and combining by stitching, knitting,crimping, punching, uniweaving, braiding, overwinding, intermeshing,comingling, aligning, twisting, coiling, knotting, and threading. 12.Curable composition comprising a support structure of claim 1 and aresin matrix component, together with catalysts, curing agents, andadditives such as fillers.
 13. Curable composition as in claim 12wherein a thermoplastic resin is present in a first amount in fluidphase as a resin matrix component and additionally is present in asecond amount in the form of the at least one flexible polymer elementin solid phase.
 14. Process for the preparation of a curable compositionas in claim 12 comprising contacting the support structure with theresin matrix component by impregnating, injecting or infusing, andmixing.
 15. Process as in claim 14 wherein injection is at ambient orelevated temperature less than the dissolution temperature.
 16. Methodfor the preparation of a composite comprising providing a curablecomposition as in claim 12, subjecting to elevated temperature for aperiod suitable for phase transition by solution of the flexible polymerelement, and subjecting to further elevated temperature for a periodsuitable for gelling and/or curing of the resin matrix.
 17. Method as inclaim 16 further comprising a degassing stage which is carried out atambient or reduced pressure.
 18. Method as in claim 16 which furthercomprises subjecting to elevated temperature in the range 100–300° C.for a period of up to 45 minutes, to effect phase transition bysolution.
 19. Method as in claim 16 wherein the gelling and/or curina isat a temperature in the range 100 to 175° C., and a post-cure is at atemperature in the range 180 to 400° C. for 1–4 hours.
 20. The supportstructure as claimed in claim 1 for use in preparing a composite foraerospace use.
 21. Support structure as claimed in claim 1 wherein theflexible polymer element has a low molecular weight adapted to react oncuring to provide a higher molecular weight for toughening.